a cog wheel is the main part that runs the cog entire body
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That is a 'cog' wheel.
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A simplistic answer is: A cog wheel is a circular disc that has
teeth round the edge. These teeth usually mesh with the teeth of
another cog. If one cog is turned, the other cog moves too. The
cogs can be made from metal or plastic.
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A cog is a wheel with projecting teeth. These can turn either
another cog or a chain.